Free tissue transfer is an increasingly utilized technique in head and neck reconstruction. Up to 15% of such transfers are unsuccessful due to anastomotic failure. Microsurgical salvage must be performed within eight hours and relies on early detection of flap ischemia and vascular thrombosis. Failure to detect vascular compromise within this time frame leads to flap necrosis, increased patient morbidity and the need for further reconstructive efforts. Present clinical methods of flap assessment are subjective, often inaccurate, and not useful for buried flaps. Tissue pH and oxygen tension appear to be the most reliable parameters of tissue perfusion and their monitoring allows early detection of anastomotic failure. We propose to develop a bedside monitoring system for continuous assessment of flap viability over an eight day period following transfer. A multiparameter, microprocessor controlled, implantable sensor will facilitate detection of anastomotic failure prior to clinical manifestations. Phase I will be devoted to the proof of concept of using such an electrode system. Electronic control and assessment of baseline drift and changes in electrode sensitivity will be utilized. Animal and preliminary clinical studies will be performed and, if successful, will lead to a Phase II proposal for reduction to clinical practice.